1. Field of the Invention
The present invention relates to an optical path folding apparatus for application to a scanner. In particular, the present invention relates to an optical path folding apparatus providing a longer optical path within the limited confines of a scanner body.
2. Description of the Prior Art
Conventional scanners use mirrors to fold an optical path one or more times, thereby reducing the dimensions of the scanner. A mirror may be used to provide light reflections, in which case the mirror is said to fold the optical path. The mirrors ultimately direct light reflected or emitted by an object to a lens set, and the lens set collects the light and projects the resulting image onto an image capturing device, for example a charge coupled device (CCD). The CCD converts the image into a digital signal for computer processing and storage.
A long optical path is desirable in order to minimize spherical aberration. However, the long optical path must conform to the desired dimensions of the scanner. The number, size, and positioning of the mirrors directly affect the size of an optical path folding apparatus, and therefore also affect the size, weight, and cost of a scanner.
The optical path of a conventional scanner may have four mirrors as shown in FIG. 1. Each mirror provides one reflection. A scanner with such an optical path folding apparatus has a feature of large volume, heavy weight and high production cost.
FIG. 2 shows another type of optical path found in conventional scanners, which employ one or more mirrors for the purpose of folding the optical path into a relatively compact configuration. Mirror M1 in FIG. 2 is a folding mirror which produces a relatively compact optical path configuration by folding a portion of the optical path into alignment with the final ray of the optical path. Additional folding mirrors may be used to further reduce the size of the optical path.
FIG. 3A shows a third type of optical path apparatus used in conventional scanners. The optical path includes multiple reflections between a pair of parallel flat mirrors, followed by a single reflection on a third mirror that directs light rays to the lens set. The use of multiple reflections between parallel mirrors can achieve a long optical path; however, it also could lead to the phenomena of xe2x80x9cghost imagesxe2x80x9d. As shown in FIG. 3B and FIG. 3C, aberrant light rays outside the desired optical path still reach the lens set and image capturing device, and thus make the captured image overlapped. A so-called xe2x80x9cghost imagesxe2x80x9d is thus produced and thereby decreases the quality of the captured image.
An object of the present invention is to solve the above-mentioned problems of the prior art by providing an optical path folding apparatus with a long optical path that does not suffer from the phenomena of ghost images.
In accordance with the object of the present invention, the optical path folding apparatus suitable for reflecting an incident light beam onto a lens set comprises a first reflection portion, a second reflection portion, a third reflection portion, a fourth reflection, a fifth reflection, and a sixth reflection portion. The first reflection portion receives the incident light beam and reflects a first light beam. The second reflection portion receives the first light beam and reflects a second light beam. The third reflection portion receives the second light beam and reflects a third light beam. The fourth reflection portion receives the third light beam and reflects a fourth light beam. The fifth reflection portion receives the fourth light beam and reflects a fifth light beam. The sixth reflection portion reflects the fifth light beam onto a lens set. The first reflection portion and the fifth reflection portion are coplanarity and can be located on a first mirror. The second reflection portion, fourth reflection portion and sixth reflection portion are coplanar and can be located on a second mirror.
In the optical folding apparatus of the present invention, light is reflected six times. Thus, a relatively long optical path can be obtained even when the optical apparatus is disposed in a confined space. Furthermore, the fact that the plane comprising first and fifth portions and the plane comprising the second, fourth and sixth portions are not parallel, the angle of reflection at successive reflection portions is not the same. Therefore, aberrant light rays outside the desired optical path will not reach the lens set and image capturing device. Thus, the present invention eliminates ghost images caused by optical folding apparatus using parallel mirrors.